Frequency generator system



INPUT POKER 0F FORK OUTPUT POM/ER 0F FEEDBACK AMPLIFIER July 28, 1936.

FREQUENCY GENERATOR SYSTEM B. STALLARD Filed March 6, 1934 INPUT POWER OF FEEDBACK AMPLIFIER OUTPUT POWER OF FORK OUTPUT POWER OF FORK INPUT POWER OF FEEDMCK AMPLIFIER IN l/E N TOR B. STALL/1R0 A TTORNEV Patented July 28, 1936 PATENT oFFicE FREQUENCY GENERATOR SYSTEM Burrell Stallard, Bloomfield, N. J., assignor to Bell Telephone Laboratories, Incorporated,

New York, N.- Y., a corporation of New York Application Mamh'a'1934, Serial No. 714,356

' 4 Claims. (01. 250- -36) This invention relates to frequency generator systems and more particularly to the stabilization .of frequencies of these systems. a An object of this invention is the stabilization oi -frequencies of frequency generators.

' Another object of this invention is the regulation andvefiicient control of the amplitude of vibration of the mechanical elements of mechanically controlled oscillators.

.Another object of this invention is the facilitationof starting ofregeneratably driven forks employed in frequency generators.

:.-The stabilization of the frequency of the current of the output of frequency generators is highly :desirable in telephoto and other systems 'inwhi'ch precise synchronization isrequired. Due

to changes in circuit conditions and other causes variations in frequency of thecurrent produced by mechanically controlled oscillators employed in these systems occur in relatively short periods of time. The variation in the amplitude of vibrations of the mechanical member of this type of oscillator causes an increase ordecrease in the frequency in the output of the generator. An increase in the amplitude of vibration of the me- :chanical member produces a decrease in frequency, while a decrease in the amplitude of vi- -bration results in an increase in frequency.

'Changes in the condition of the circuit, such as thepower supply, are chiefly responsible for the variations in the amplitude of vibration of the mechanical members. 7. In accordance with this invention, the anodecathode impedance of a space discharge device rcontrolled by the varying potential of the control electrode of the device maintains the output power of these oscillators relatively constant. The anode-cathode impedance is associated with the circuit for the supply of power to the mechanical member, and by means of thepotential electromotive force of the circuit does not exceed avalue which produces an increase in power, a decrease'in the amplitude of vibration of the mechanical member and an increase in the frequency of current of the oscillator. When the electromotiveforce of the circuit increases above :this predetermined value, the impedance de- Qcreases rapidly and a fairly large proportion of th current of the circuit passes through the impedance. As a consequence, the power supply to the mechanical member of the oscillator is maintained relatively constant by this impedance.

In a tuning fork oscillator of the conventional type comprising a tuning fork, a driving and driven element and an amplifier, the anodecathode impedance of the space discharge device is bridged across the amplifying circuit to which .the driving element is coupled. The potential of the control electrode of the device varies directly with the fluctuation of the electromotive force produced by the amplifier. However, the control electrode is biased to prevent any appreciable current passing through the anode-cathode impedance until the electromotive force of the oscillator exceeds the limit necessary for the optimum range of the mechanical member. This limit may be varied by means of a variable resistance or potentiometer which controls the biasing potential. Any increase in the electromotive force of the amplifier abovev the limit produces a rapid decrease in the anode-cathode impedance. The proportion of the current of the amplifier passing through the impedance is markedly increased while the proportion passing through the driving element of the oscillator decreases. Accordingly, when the electromotive force of the amplifier remains below the selective predetermined limit, practically all of the current of the amplifier passes through the driving element. When the electromotive force exceeds this limit, approximately the same current passes through the driving element, the surplus current being absorbed by the impedance. Regardless of the value of the electromotive force produced by the amplifierand its fluctuation due to variations in the current supplied for the anode of the amplifier, a relatively constant current is applied to the drivingelement. The control of the power delivered to the driving element limits the variation of vibration of the amplitude of the fork and as a result, the frequency of current of the oscillator is stabilized.

A more comprehensive understanding of this invention may be obtained by reference to the drawing in which:

;Fig. 1 is a schematic diagram of anapplication of the invention in a tuning fork oscillator;

Fig. 2 illustrates diagrammatically the effect that small changes in the power supply of a meichanically controlled oscillator produces in the amplitude of vibration of the mechanical memithenmplitude of vibration of the mechanical through the transformer 1 to the space discharge 4 device H5 in which they are further amplified. n

The amplified waves are transmitted through the transformer H to the driving'coil 2' to actuate in a well known manner the tuningforkfi. g

Bridged across the circuit of the oscillator between the space discharge devices 5 and I6 is a space discharge device 8. The anode-cathode impedance of this device is connected across the circuit. The anode 22 of the device iscdnnectted to one-side of the circuit through the'condenser 9,

while the cathode 20 is connected tothe other side The control electrode 2! of the of the circuit. device is connected to the same side of the circuit as the anode 22; The: battery lz furnishes the biasing potential for the control electrode 2| through the potentiometer 'l l. The biasing potential may be changed when desired by means of the potentiometer H. 9 a

'The space current for the'devices 5, 8, and. I6

is supplied by the battery IS. A series impedance coil I is provided through which the space'current passes to the anode 22 of the spacedischarge device 8. The biasing potential for the control electrode of device I6 is furnished by battery l through resistance l4, while that for the control electrode of the devic'e5 is supplied by the battery 7 6. -A blocking condenser 13 serves to prevent directcurrent fromthe output circuits of devices '5 and Bfrom being impressed on the controlelectrode of space discharge device i6. Acondenser i9 is inserted in the circuit between the secondary of transformer H and the'driving coil 2. Cathode heating current for devices '5, -8 and I 6 is-supplied b'y/batteries 30, 3|, and'32, respectively." 7

Variable condenser 35 in inserted in series with the drivingor pick-up coili- The function of this condenser is to compensate partially for the difference in physical dimensions of diiferentforks for the production of the desired frequency or for changes produced in'the same fork-as it ages. By adjusting thecapacity of the condenser the necessity of filing a new fork or a fork. the characteris'tics of which have changed; is-avoided.

The :operation of theoscillator is as follows: Thevibrationsof the tuning fork'3 are induced in the winding of the 'dri'ven'member 'l and after passing through transformed 4 are amplified by the space discharge device 5. The amplifiedjcurrent passes through thesecondary winding of the transformer i. The anode-cathode impedance of the space discharge device 8 aifords one path for "the amplified current, while another path leads to the input of space discharge device l6. The

potential bias of thecontrol'electrode is sufficient to prevent'any appreciable amount of current 'passingthrough the anode-cathode impedance of I the space discharge device 8. This bias is so regu- :lated by means of the potentiometer II that the anode-cathodeimpedance is infinitely high until thepotential of the control electrode exceeds a predetermined limit, This limitais determined by. ascertaining the value of the electromotive force produced in the. winding of the secondary 1" pressedcn the secondary of the transformer'l passes through this impedance and a'lesser pro- .p01tion passes through the device 16. Expressed tion of this invention in the stabilization of the frequency. of an oscillator is more readily demon- 2,049,179 of the transformer above which the power output of the amplifier causes variations in the amplitude of vibration of the fork 3. If, due to physical changes in the fork, a'dilferent amplitude of the fork is necessary than that previously .5 required or if a different frequency is desired, the circuit may be stabilized at the frequency desired by changing the bias of the control electrode by'means of the potentiometer ll. When the predetermined value of the electromotive 10 force is exceeded, the potential of the controlelectrode 2! increases and the anode-cathode impedance of the device is suddenly decreased. Accordingly, a greater proportion of the currentimdifferently the increase of potential of the control electrode 2! above the operating. point of the space dischargedevice results in the passage of current 26 fromithe anode 22 to the cathode 20. :Theoutput I current so producedis 180 degrees out: of phase with that of the input from the secondary of transformer I. This condition prevents further increase in the power to. the input of the space 25 a discharge device I6. :As a consequence the input power to the device I6 is maintained at afairly constant value. T

The current is further amplified by the space discharge device l6. and passes through the transformerl'l to the driving. element 2. The power delivered to the driving element 2 due to the' stabilization actionof deviceB remains constant. I Theoperation of. the} oscillatorand the funcstrated by reference to Figs. 2 and 3. H U Fig. 2 shows the relationship between the input and output power. of a single linear amplifier employed in a tuning fork oscillator withoutfthe stabilization circuit of this invention and the correlation between the input andoutput power of the tuning fork ofthis oscillator. Curve a represents the relation between the inputand: output of the amplifier'that exists for the production of the frequency desired- Curve 0 shows theoutput power of the fork produced by varying the input power. In curve bthe relation between theinput'and outputpower of the, amplifier isshown when'the circuit'conditions of the .amplifier have 5!) changed. These changes may be due. to decreases in the current supply for the anode. of the x space discharge devices employedin the-amplifier. Theparticular relationof the input and output power of the amplifier at which the fork' operates is the intersection 'A and Bof the am--' plifier power curve a or b and'the'fork'power curve c'sincejat these pointsiequilibrium is attained. I y i v :j I

Fig. 3-shows the. relativeoutput of the amplifier and fork of the oscillator produced by {the input .of the amplifier and fork. in theoscillator' shown in Fig. 1. put, power of the amplifier which insures the production of a current the frequency of which .65 is desired, while curve 12' shows therelationship between the input Iandoutputpowerof 'the arnplifier when thepc'urrent conditions of the ampli- Curve represents theinputand outfierhave changed. "curve c" shows the corr'la tion between the input and output power of thew fork employed in thefoscillator. The fork opera ates at point A' or B fdepending gupon whether. 7 the input-'output-power characteristics "of the amplifier is that represented by curve a or b The change in the power relation between curve a to curve I) in Fig. 2 shifts the operating point on the fork curve from point A to point B. A substantial increase in the power of the fork accordingly results. A marked decrease in the amplitude of vibration of the fork follows with a consequential increase in the frequency of current of the oscillator. With the stabilization effected by the space discharge device 8, however, the variations in the input and output power relation of the amplifier from curve a to curve I) of Fig. 3 produces little change in the operating point of the fork as indicated by points A and B on the fork curve. Since little variation in the power of the fork results, the amplitude of vibration of the fork and the frequency of current of the oscillator are stabilized.

An important advantage inherent in this invention is that the fork or other vibratory element starts from rest when the power characteristics of the oscillator are those represented in Fig. 3. The mechanical member of an oscillator, the power characteristics of which are shown in Fig. 2, does not start from rest unless the amplification is so great that the mechanical member is normally driven at a considerable increase in amplitude which results in a decrease in frequency stability.

The particular embodiment described is illustrative and is not to be construed as a limitation of the scope of the invention. Various modifications utilizing the principle of this invention for the control of the amplitude of vibration of mechanical vibratory elements or for the stabilization of frequency of mechanically controlled oscillators, such as piezoelectric crystal oscillators and other oscillators may be employed without diverting from the scope of this invention.

What is claimed is:

1. In combination, a mechanically controlled oscillator comprising a mechanical vibratory member, a driving element for actuating said member, an electric discharge amplifier for supplying power to said element and a space discharge device controlled by the electromotive force generated by said amplifier for maintaining the power supplied by said amplifier to said element relatively constant.

2. In combination, a mechanically controlled oscillator comprising an amplifier having an input circuit, stabilizing means comprising a space discharge device including an anode-cathode impedance and a control electrode for maintaining the frequency of currents of said oscillator relatively constant, means for applying the electromotive force generated in said input circuit to said control electrode to vary said impedance, and means controlling said stabilizing means for varying the frequency of oscillations of said oscillator for which stabilization is effected.

3. A tuning fork oscillator comprising a tuning fork, a driving coil, a pick-up coil, an amplifier having an output circuit connected to said driving coil and an input circuit connected to said pick-up coil, said amplifier comprising two electric discharge devices, a pair of conductors connecting said electric discharge devices in cascade, a space discharge device comprising anode, cathode and control electrode bridged across said pair of conductors between the two said electric discharge devices of said amplifier, the anode and control electrode of said space discharge device being connected to one side of said pair of conductors and the cathode being connected to the other side of said pair of conductors, a source of biasing potential for said control electrode and means for varying said biasing potential.

4. A mechanically controlled oscillator comprising a mechanical vibratory element, an amplifier having input and output circuits coupled to said vibratory element for the production of sustained oscillations, a space discharge device comprising an anode-cathode impedance bridged across said input circuit and a control electrode and means including said control electrode for varying said impedance in accordance with the electromotive force generated in said input circuit for maintaining the energy supplied to said output circuit relatively constant.

BURRELL STALLARD. 

